SDL is a library that allows you portable
low-level access to a video framebuffer, audio
output, mouse, and keyboard. With SDL, it is easy
to write portable games which run on many
different platforms.

Vendetta Online is a multi-platform 3D space-combat MMO for Windows, Mac, Linux/32 and Linux/64. The game permits players to interact in a vast online galaxy; fighting, trading, and mining their way to success. A "twitch" type real-time combat model makes true player skill the deciding factor instead of character advancement. Massive capital-ship battles shake the foundations of the major nations at war, while others struggle to push back the encroachment of the AI "Hives". A no-strings free trial is available.

Wine is an implementation of the Windows API on top of X and Unix. It
does not require Microsoft Windows, but can use native Windows DLLs if
they are available. It provides both a development toolkit for porting
Windows source code to Unix as well as a program loader, allowing many
unmodified Windows programs to run on x86-based Unixes.

GCompris is an educational software suite with numerous activities for children aged 2 to 10. Some of the activities are game-orientated, but nonetheless still educational. These include computer discovery (keyboard, mouse, different mouse gestures), algebra (table memory, enumeration, double entry table, mirror image), science (the canal lock, the water cycle, the submarine, electric simulation), geography (place the country on the map), games (chess, memory, connect 4, oware, sudoku), reading practice, and others (learn to tell time, puzzles of famous paintings, vector drawing, cartoon making, etc.). It currently offers in excess of 100 activities, and more are being developed.

XMLTV is a set of programs to obtain and process
TV (tvguide) listings and manage your TV viewing.
It stores the listings in an XML-based format and
most of the programs are filters which read and/or
write XML. It includes tools to obtain, sort,
grep, print, and munge listings, and two end-user
programs to plan a week's TV viewing.

KNOPPIX is a bootable CD with a collection of GNU/Linux software,
automatic hardware detection, and support for many graphics cards,
sound cards, SCSI devices, and other peripherals. It can be used as a
Linux demo, educational CD, rescue system, etc. It is not necessary to
install anything on a hard disk due to on-the-fly decompression.

Freeciv is a multiuser reimplementation for Unix/X of the famous Microprose game of Civilization. By default, the game is an improved Civ II, but this can be customized; modpacks for near-100% compatibility with Civ I and Civ II are included. Multiuser gameplay is real-time: in each turn, all human players move concurrently. The game is designed to remain fairly playable even on poor network connections. Freeciv can also be played on standalone machines, and its AI players are a good challenge for beginners. The source code comes with the server, two X clients, and non-X clients for MS Windows and Amiga. Freeciv is released under the GNU General Public License. It is maintained by an international team of coders and enthusiasts, and is easily one of the most fun and addictive network games out there.